Isolation and physical characterization of membrane proteins remains a central challenge in the biomolecular sciences. Isolating membrane proteins and obtaining their crystal structures is important to furthering an understanding of their function and role in metabolic pathways. Membrane proteins are difficult to manipulate and ultimately crystallize because these macromolecules are rarely soluble in simple aqueous buffers. The lack of efficient methods for isolating, purifying, and crystallizing membrane proteins represents a significant hindrance to fundamental and applied biological research because these proteins perform so many crucial functions in vivo.
Solubilizing membrane proteins for physical characterization and crystallization requires that the membrane protein be combined with a synthetic amphiphile, typically a detergent. The resulting crystal is generally a protein-detergent complex rather than solely the isolated protein. The detergent therefore plays an important role in determining whether high quality crystals will form. High quality crystals are essential for structural determination and characterization, such as by X-ray crystallography.
Determining the three-dimensional structure of membrane proteins has been successful only within the past two decades. Thus, the set of known membrane protein structures is far smaller than the set of known soluble protein structures. Synthetic amphiphiles are used to extract embedded proteins from the membranes in which they naturally occur and to maintain native protein conformation in the solubilized state. Physical characterization is often carried out with protein-amphiphile complexes. Such complexes are usually the basis for crystallization efforts. The ability to grow high quality crystals is typically the rate-limiting step in structure determination. Thus, synthetic amphiphiles that can aid crystal formation are crucial tools in this field.
In view of the limited detergents available for solubilizing and stabilizing membrane proteins, there exists a need in the field for alternative detergents with expanded and/or unique protein solubilizing and stabilizing properties. Thus, new amphiphiles for solubilizing and stabilizing membrane proteins are needed to aid fundamental and applied protein research. Preferably the amphiphiles could be synthesized from readily available starting materials and would solubilize membrane proteins at lower concentrations of the amphiphile than are needed for currently available detergents such as CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate) and CHAPSO (3-[(3-cholamidopropyl)-dimethylammonio]-2-hydroxy-1-propanesulfonate).